Extracellular polymeric substances (EPS) producing and oil degrading bacteria isolated from the northern Gulf of Mexico

Sinking marine oil snow was found to be a major mechanism in the transport of spilled oil from the surface to the deep sea following the Deepwater Horizon (DwH) oil spill. Marine snow formation is primarily facilitated by extracellular polymeric substances (EPS), which are mainly composed of proteins and carbohydrates secreted by microorganisms. While numerous bacteria have been identified to degrade oil, there is a paucity of knowledge on bacteria that produce EPS in response to oil and Corexit exposure in the northern Gulf of Mexico (nGoM). In this study, we isolated bacteria from surface water of the nGoM that grow on oil or Corexit dispersant. Among the 100 strains isolated, nine were identified to produce remarkable amounts of EPS. 16S rRNA gene analysis revealed that six isolates (strains C1, C5, W10, W11, W14, W20) belong to the genus Alteromonas; the others were related to Thalassospira (C8), Aestuariibacter (C12), and Escherichia (W13a). The isolates preferably degraded alkanes (17–77%), over polycyclic aromatic hydrocarbons (0.90–23%). The EPS production was determined in the presence of a water accommodated fraction (WAF) of oil, a chemical enhanced WAF (CEWAF), Corexit, and control. The highest production of visible aggregates was found in Corexit followed by CEWAF, WAF, and control; indicating that Corexit generally enhanced EPS production. The addition of WAF and Corexit did not affect the carbohydrate content, but significantly increased the protein content of the EPS. On the average, WAF and CEWAF treatments had nine to ten times more proteins, and Corexit had five times higher than the control. Our results reveal that Alteromonas and Thalassospira, among the commonly reported bacteria following the DwH spill, produce protein rich EPS that could have crucial roles in oil degradation and marine snow formation. This study highlights the link between EPS production and bacterial oil-degrading capacity that should not be overlooked during spilled oil clearance.深水地平线（Deepwater Horizon, DwH）原油泄漏事件后，沉降性海洋油雪被证实是溢油从海面向深海输运的关键机制。海洋雪的形成主要依赖胞外聚合物（extracellular polymeric substances, EPS），这类物质主要由微生物分泌的蛋白质与碳水化合物构成。尽管已有诸多细菌被证实可降解原油，但目前学界对墨西哥湾北部（northern Gulf of Mexico, nGoM）中响应原油与科赛特（Corexit）分散剂暴露并产生EPS的细菌认知仍较为匮乏。本研究从墨西哥湾北部的表层水体中分离出可在原油或科赛特分散剂上生长的细菌。在所分离的100株细菌中，有9株被证实可产生大量EPS。16S rRNA基因分析结果显示，6株分离菌（C1、C5、W10、W11、W14、W20）隶属于交替单胞菌属（Alteromonas）；其余菌株分别与海螺旋菌属（Thalassospira，C8）、海滨杆菌属（Aestuariibacter，C12）以及埃希氏菌属（Escherichia，W13a）具有较近亲缘关系。相较于多环芳烃（0.90%~23%），分离菌对烷烃的降解效果更优（17%~77%）。本研究检测了在原油水可溶组分（water accommodated fraction, WAF）、化学强化水可溶组分（chemical enhanced WAF, CEWAF）、科赛特分散剂以及对照组条件下的EPS产量。可见聚集体的产量在科赛特分散剂处理组中最高，其次依次为化学强化水可溶组分组、原油水可溶组分组与对照组，这表明科赛特分散剂总体上可促进EPS的产生。原油水可溶组分与科赛特分散剂的添加并未改变EPS中的碳水化合物含量，但可显著提升其蛋白质含量。平均而言，原油水可溶组分与化学强化水可溶组分处理组的EPS蛋白含量是对照组的9~10倍，而科赛特分散剂处理组的蛋白含量则为对照组的5倍。本研究结果表明，在深水地平线原油泄漏事件后常见的细菌类群中，交替单胞菌属与海螺旋菌属可产生富含蛋白质的EPS，这类物质在原油降解与海洋雪形成过程中可能发挥关键作用。本研究揭示了EPS产生与细菌原油降解能力之间的关联，该关联在溢油清除过程中不容忽视。